stormwater management plan proposed 7 eleven service station · the collected water will be used...

2

Stormwater Management Plan Proposed 7 Eleven Service Station

Eastern Road, Rooty Hill NSW 2766

CONTENTS

1.0 INTRODUCTION………………………………………………………………………… 3

2.0 STORMWATER CONCEPT……………………………………………………….……. 4

3.0 STORMWATER QUANTITY MANAGEMENT………………………………………... 5

4.0 STORMWATER QUALITY MANAGEMENT………………..………………………... 5

5.0 OVERLAND FLOW PATHS ………………………………..………………………... 7

6.0 CONCLUSION……………………………………………………..…………………..…... 7

APPENDIX A – MUSIC Model

APPENDIX B – Summary Sheets

3



Site

1.0 INTRODUCTION

Richmond and Ross Pty Ltd, Consulting Engineers, were engaged to carry out a Stormwater Management

Plan for the proposed service station at Eastern Road, Rooty Hill, NSW 2766. This report addresses the

management of stormwater, within the proposed site boundaries.

The below assessment is based on site survey, hydraulic and hydrological calculations with respect to

the proposed development works and in accordance with

• Blacktown DCP 2015 – Part J

• Developer Handbook for Water Sensitive Urban Design

Reference should also be made to the civil drawings within the DA package.

The site forms part of an overall development which is subject to a subdivision development application.

1.1 SITE DETAILS

The area being developed for the service station has a total area of approximately 1,985m2 and is

currently used as a carparking area for the adjacent sports' fields.

Figure 1 - Aerial Photograph of site location

4



1.2. PREVIOUS REPORTS

As part of the subdivision DA, Cardno have prepared a flood report for the site (80218006:VJ –

31/5/2018 with an updated assessment in 21/01/19). The flood report calculated a 1% AEP flood

depth for the site of RL 33.9. Council have advised that for the purposes of a flood planning level, a

1% AEP flood level of 34.2mAHD should be adopted.

Council’s engineering guide and DCP Part A states freeboard requirements for industrial and

commercial developments to be 300mm above the 1% Flood Levels. Therefore, the proposed finished

floor level is 34.5 m AHD to meet the freeboard requirements.

Cardno have also prepared an engineering assessment report (80218006 28/5/2018). In particular, this

report addresses issues of stormwater quantity for the overall development and provides a detention

basin to cater for the ultimate developed state of the site as part of the interallotment drainage system.

No additional OSD measures are proposed for the 7 Eleven site.

2.0 STORMWATER CONCEPT

It is proposed to build a service station with a shop building, a fueling canopy and associated and

associated customer parking. Entry to the site is from Eastern Road and from a circulation lane

through adjacent carparks to the west.

• Stormwater from shop building roof, canopy roof and pavement drains to a new underground

pipe network;

• Proposed roof area is approx. 530m2. 220m2 of building roof will be directed to a 4000L

above ground rainwater tank. The collected water will be used for toilet flush and bioretention

basin irrigation within the site. Overflow from the tank will be connected to the site’s

underground stormwater network and surcharge into Bio Basin C for treatment. Analysis by

MUSIC indicates that 80% of the estimated potable water requirement is provided by this

arrangement. 310m2 of the canopy roof surcharges in Bio basin C.

• Bio retention basins are proposed to filter the majority of the runoff.

• A Stormceptor is proposed to treat stormwater prior to it leaving the site. This is to achieve

two purposes. The first and main purpose is to capture hydrocarbons and satisfy council's

requirements for a GPT specifically targeting hydrocarbons (service station classified as a

high-risk development).

The stormceptor also assists in TSS removal for flows that bypass/overflow past the bio basins

5



• The development connects to the proposed interallotment drainage system. Reference should

be made to the subdivision DA drawings for additional details.

3.0 STORMWATER QUANTITY MANAGEMENT

A detention basin is provided at the downstream end of the interallotment drainage system as part of

the overall subdivision. This basin has been sized by Cardno to cater for the developed sites and no

additional measures are required on the McDonald's site.

4.0 STORMWATER QUALITY MANAGEMENT

A stormwater quality improvement train is proposed as follows-

4.1 Rainwater Tank

The rainwater is designed to allow the reuse of collected rainwater for toilet flushing and garden

watering. Reuse has been estimated as 0.1kl/day for toilet flushing (1 pans x 0.1kl/day) and

11.6kl/year scaled as PET-Rain for irrigation (29m2 x 0.4kl/year/m2 bio). Referring to WSUD

guidelines, only irrigation of bio basins is required to be modelled. The remaining landscaped area

proposed to be turfed do not have to be modelled.

A 4kl rainwater tank has been proposed which has been modelled within MUSIC as having 3.2kl

capacity.

4.2 Gross Pollutant Traps (GPT’s)

A Stormceptor S.300/250.C1 is proposed. The purpose is to –

• Satisfy BCC's requirement for a specific treatment measure for total hydrocarbons. The

proposed model has been designed for a minimum 2EY (75% of the 1EY). The proposed

model has a treatment flow rate of 35l/s whereas the 2EY flow rate from the development is

31.9l/s (0.75 x 77 x 1985 x 0.000278).

• Provide additional TSS removal for area that bypass/overflow from the bio basin.

4.3 Bio retention basins

3 bio retention basins are proposed and are shown on the civil drawings. Reference should be made to

the drawings for sizes and locations. Due to constraints from the existing inter-allotment 600dia

stormwater drainage line, the subsoil drain in Bio basin A and B had to be directed to a separate

discharge point compared to the overflow. Discussion with council engineer has confirmed that the

subsoil drain is not required to pass through the stormceptor and therefore it discharges directly to pit

6



D. Overflows are collected by shallow pits and the outlet pipes of these cross over the existing

stormwater line. Refer Section D in DWG C04. Bio basin A and B have a connected submerged zone.

4.4 Water Quality Outcome – MUSIC Modelling

MUSIC modelling was undertaken for the proposed treatment train. The model was set up using the

latest MUSIC-Link data and in accordance with BCC requirements. A copy of the MUSIC link

summary sheet is included in the appendices.

Figure 2: Treatment train and Pollution Removal as modelled in MUSIC

The removal rates calculated for the treatment train are as follows-

Source Residual % Reduction Target

TSS 328 34 89.6 85

TP 0.601 0.172 71.3 65

TN 3.08 1.62 47.3 45

GP 33.5 0.096 99.7 90

A copy of the MUSIC link summary sheet is included in the appendices.

5.0 OVERLAND FLOW PATHS

7



The site generally grades towards the east and flows will generally run along the frontage of the site

towards Eastern Road. Reference should be made to the Cardno flood report for overall flow paths.

6.0 CONCLUSION

We believe that the proposed system satisfies the relevant requirements of Blacktown Council for

stormwater.

A



APPENDIX A – MUSIC MODEL

A



APPENDIX B – Summary Calculations

Project Details

Project: 7 Eleven Blacktown

Report Export Date: 24/06/2020

Catchment Name: 200056 - 7-Eleven-Blacktown (With Bio)V2

Catchment Area: 0.197ha

Impervious Area*: 138.0%

Rainfall Station: 67035 LIVERPOOL(WHITLAM

Modelling Time-step: 6 Minutes

Modelling Period: 1/01/1967 - 31/12/1976 11:54:00 PM

Mean Annual Rainfall: 857mm

Evapotranspiration: 1261mm

MUSIC Version: 6.3.0

MUSIC-link dataVersion: 6.33

Study Area: Blacktown

Scenario: Blacktown Development

Company Details

Company: Richmond & Ross Consulting Engineers

Contact: Harshad V

Address: Level 1, 38 Willoughby Rd, Crows Nest, 2065

Phone: 02 9490 9600

Email: [email protected]

Treatment Train Effectiveness

Node: Post-Development Node Reduction

Flow 7.69%

TSS 89.5%

TP 71.3%

TN 47.3%

GP 99.7%

Treatment Nodes

Node Type Number

Rain Water Tank Node 1

Bio Retention Node 2

GPT Node 1

Source Nodes

Node Type Number

Urban Source Node 8

MUSIC-link Report

* takes into account area from all source nodes that link to the chosen reporting node, excluding Import Data Nodes

Comments

Roof areas do not have baseflow. Therfore, the invalid results for roof areas can be ignored

NOTE: A successful self-validation check of your model does not constitute an approved model by Blacktown City CouncilMUSIC-link now in MUSIC by eWater – leading software for modelling stormwater solutions

1 of 3

Passing Parameters

Node Type Node Name Parameter Min Max Actual

Bio Bioretention A+B (18m�) Hi-flow bypass rate (cum/sec) None None 100

Bio Bioretention A+B (18m�) PET Scaling Factor 2.1 2.1 2.1

Bio Bioretention C (11m�) Hi-flow bypass rate (cum/sec) None None 100

Bio Bioretention C (11m�) PET Scaling Factor 2.1 2.1 2.1

GPT Stormceptor Interim Blacktown Node 2013-05-28 Hi-flow bypass rate (cum/sec) None None 0.035

Post Post-Development Node % Load Reduction None None 7.69

Post Post-Development Node GP % Load Reduction 90 None 99.7

Post Post-Development Node TN % Load Reduction 45 None 47.3

Post Post-Development Node TP % Load Reduction 65 None 71.3

Post Post-Development Node TSS % Load Reduction 85 None 89.5

Rain Rainwater Tank % Reuse Demand Met 80 None 83.9913

Urban Building roof (220m�) Area Impervious (ha) None None 0.022

Urban Building roof (220m�) Area Pervious (ha) None None 0

Urban Building roof (220m�) Total Area (ha) None None 0.022

Urban Bypass Landscaping (50m�) Area Impervious (ha) None None 0

Urban Bypass Landscaping (50m�) Area Pervious (ha) None None 0.005

Urban Bypass Landscaping (50m�) Total Area (ha) None None 0.005

Urban Canopy roof (310m�) Area Impervious (ha) None None 0.031

Urban Canopy roof (310m�) Area Pervious (ha) None None 0

Urban Canopy roof (310m�) Total Area (ha) None None 0.031

Urban Landscaping (80m�) Area Impervious (ha) None None 0

Urban Landscaping (80m�) Area Impervious (ha) None None 0

Urban Landscaping (80m�) Area Pervious (ha) None None 0.008

Urban Landscaping (80m�) Area Pervious (ha) None None 0.008

Urban Landscaping (80m�) Total Area (ha) None None 0.008

Urban Landscaping (80m�) Total Area (ha) None None 0.008

Urban Pavement Areas (220m�) Area Impervious (ha) None None 0.022

Urban Pavement Areas (220m�) Area Pervious (ha) None None 0

Urban Pavement Areas (220m�) Total Area (ha) None None 0.022







Only certain parameters are reported when they pass validation


2 of 3

Failing Parameters

Node Type Node Name Parameter Min Max Actual

Urban Building roof (220m�) Baseflow Total Nitrogen Mean (log mg/L) 0.32 0.32 0.11

Urban Building roof (220m�) Baseflow Total Phosphorus Mean (log mg/L) -0.82 -0.82 -0.85

Urban Building roof (220m�) Baseflow Total Suspended Solids Mean (log mg/L) 1.1 1.1 1.2

Urban Canopy roof (310m�) Baseflow Total Nitrogen Mean (log mg/L) 0.32 0.32 0.11

Urban Canopy roof (310m�) Baseflow Total Phosphorus Mean (log mg/L) -0.82 -0.82 -0.85

Urban Canopy roof (310m�) Baseflow Total Suspended Solids Mean (log mg/L) 1.1 1.1 1.2

Only certain parameters are reported when they pass validation


3 of 3

stormwater management plan proposed 7 eleven service station · the collected water will be used...

Documents